Good point you make there Colin,
I've had a look in my parts book, but mine doesn't have any pictures of the optional extras. But it does list TWO tow bar assemblies.
366772 - Tow bar complete assembly for cars fitted with rear bumper overriders (same part number as in your diagram)
366460 - Tow bar complete assembly for cars NOT fitted with rear bumper overriders (presumably the straight one, likely to be cheaper!)
so there are definitely two Rover spec versions.
Bri.